Dynamo-electric machine.



No. 898,228. PATENTED JULY 14, 1908. G. S. DUNN.

DYNAMO ELECTRIC MACHINE. APPLICATION FILED FEB. 11, 1905.

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Witnesses I Inventor- Wkazi arm S; Dunn- No. 893,228. PATENTED JULY14, 1908.

G. S. DUNN.

DYNAMO ELECTRIC MACHINE.

APPLICATION FILED FEB. 11, 1905.

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WWJWaZL Game ,3. Dunn,

UNITED STATES PATENT OFFICE.

' GANO S. DUNN, OF EAST ORANGE, NEW JERSEY, ASSIGNOR TO GROOKER-WHEELER COMPANY,

OF AMPERE, NEW JERSEY, A CORPORATION OF NEW JERSEY.

DYNAMO-ELECTRIC MACHINE Specification of Letters Patent.

Patented Jul 14, 1908.

To all whom it may concern:

Be it known'that I, GANO S. DUNN, a c1t1- zen of the United States of America, and a resident of East Orange, county of Essex,

and State of New Jersey, have invented certain new and useful Improvements in Dynamo-Electric Machines, of which the following. is a specification.

This invention relates to modifications introduced in dynamo-electric machines, and the method. of introducing such modifica tions to reduce and prevent audible vibrations or humming, particularly in connection with those'forms" of machines wherein annular frames, or yokes sup ort the cores for the field-magnets, and t e yokes and pole-horns of the ole-shoes have for struc tural and electrica reasons been so modified that there is an increase in the tendency to I vibrate audibly.

give the requisite cross-sectionto carry the magnetic lines, and the thickness has usually a proximated "to that of the width, so that t h stiffness to resist vibration, or any deformation from its original circular form. I have found it desirable to depart materially from this type of. machine with a thick and rigid yoke, in developing a closed or'semi-closed type of machine, by extending the oke in t e direction of its axis, so that it w' 1 essentially shield the field-coils and armature, and be in this sense an inclosing yoke for the armature and fields, and the addition of end shieldsof sim le form will effect a complete vinclosure of t e electrical parts of the ma; In so doing, substantially the same.

chine. cross-sectional area is referably preserved, in order to avoid additionalweight and material in the frame. This necessitates a material reduction in the thickness of the yoke, so that the yoke is, in effect, a comparatively thin annular shell or band, and it becomes e yoke would possess considerable particularly thin when cast-steel is used.

' But, on using with and supporting from thistype of yoke inwardly projecting poles with po e-shoes and pole-horns of the proportions heretofore used, the shell a pears to have resonating properties, and vibrations are set ,up in the magnet-poles by reason of the insufficient stiffness of the yoke for the support of the cores of the magnet-poles and by the fluctuating mechanical action caused by the fluctuating magnetic flux between the armature teeth and pole-horns as the teeth approach and leave the horns. This results in a humming noise of such intensity as to render the machine commercially undesirable.

The thicknesses of the pole-horns of the pole-shoes which project over the edges of the cores have also been modified by making the ole-horns thinner, as this ermits an equa reduction in the outside ,iameter of the machine with the consequent saving of weight and material. It is also carried to such an extent as to bring about, when the machine is running, a considerable degree of ma netic saturation which cannot be material y increased by any reactions of the armature. In this way distortion of the field under load is materially reduced, but reduction in thickness increases the susceptibility of the horns to vibration, and to vi rations at periods within the auditory range.

The objectionable audible vibrations'which result from either or both of the above defined modifications, when other parts are reserved with the usual proportions, can, I d, be substantially eliminated, first, by increasin the dimensions of the cores in the circu erential direction of the machine, and, second, by. so modifying the air-gaps that there will be extended arcs of ap roach and recession under the pole-shoes wit suitably graduated increase or diminution of the magnetic flux between the pole-shoes and transverse section through the machine on the line IIII of Fig. 1, one of the pole-shoes and pole-horns being partly broken away.

3 shows the outline of a pole-shoe and its relation to the armature face together with construction lines which accurately indicate its form and the theory of construction. Fig. 4 is a curve diagram illustrating the modification in the air-gaps.

The invention herein claimed, is illustrated by drawings carefully made to scale of a direct-current machine rated at one horse power, and having an outside diameter of 12% inches, but machines have been developed in various sizes ranging from one-fourth to three horse power, and they are chiefly used as electric motors. A cast-steel or cast-iron annular inclosing shell or yoke 1, which also serves as a art ofthe magnetframe, is of substantia ly cylindrical form with open ends and inwardly projecting cores 2 cast thereon. The yoke is of substantially sufficient width to cover the ends of the field-coils 3 and as illustrated is somewhat wider, with inwardly turned flanges, which to a certain extent cover the sides of the field-coils. measured radially, as on the line aa, is a comparatively small fraction of the width of the yoke measured .in the direction of the axis of the machine, or on the line bb.

This is practicable so far as conductivity for magnetlsm is concerned, because the crosssection, which is requisite, is afforded by reason of the increased width. As an inclosing yoke of these proportions affords a less substantial support for the cores in a circumferential direction, which is the direc tion of greatest vibratory strains, I have foundit necessary to materially modify the dimensions of the cores, particularly by an increase in the thickness of each measured stiffened to suchan extent as to destroy its resonance to vibrations within the auditory range. Vibrations of the cores in a lane perpendicular to the axis of the mac line, which is the only plane in which the revolving armature would tend to set up such vibrations, are likewise prevented by the increase in base ri idity of the cores. With the increase of tiis dimensionthe thickness of the core in the direction ofthe axis of the machine as on the line d-d is correspondingly reduced, so that the cross-section will not exceed what is required for magnetic conductivity for the sake of economy of material in the surrounding field-coils. This results in a core wherein the dimension in the direction of the circumference of the machine exceeds the dimension in the direction of the axis of the machine.

An armature 4, the coils of which lie between the teeth and in the slots of alami- The thickness of the yoke origina thickness is allotted to these pole-horns must be allowed for in the outside diameter of the machine. As this is expensive, the thickness iskept down as much as possible, for

example, to the dimensions indicated by the line ee. In adjusting this thickness, the magnetic conductivity is brought up to about the point of saturation to counteract the tendency to distortion of the field by armature reactions when the machine is running under load. But this weakens the pole-horns, and renders them subject to vibration. The distance apart of the ti s and the thickness of the pole-horns being liked by the electrical consideration above referred to, it follows that the length f of each ole-horn is de pendent on the wi th of the ody portion of the field-core measured in the direction of the circumference of the machine, this being the same as the similar dimension of the core to which the pole-shoe "is attached. Increase in this dimension of the core, above discussed with respect to the stiffening of the core and yoke, therefore, also results in a shortening and consequent, stiffening of the ole-horns so that they will not vibrate audifily.

The field-coils are wound upon forms to the sha e illustrated in 1, but the coil as fly Wound is flat, each convolution being substantially in a plane for convenience in winding, as it is not practicable to give the coils the additional curvature or bowed form illustrated in Fig. 2, in the process of winding. If the field-cores had been of the usual proportions with their greatest dimensions in the direction of the axis of the machine and their dimensions in the circumferentialdirection of the machine ke t as small as possible, the field-coils could e left straight instead of bowed, or bent but sli htly. Butwith the dimensions of 'the fie d-cores modified as herein set forth, this additional curvature becomes necessary to save space and material at the base of the core. This curvature is given to the coils after winding by forcibly bendin them to the bowed form shown in Fig. 2, efore setting them in place on the cores in the machine.

In addition to the modifications above discussed indetail, the purpose of which is to site the pole-shoes.

such are imposed, it is a further object of the invention to mitigate the cause of vibration so far as'possible, which is due to the suctaperin the air-gaps at the pole-horns or termina sections of the air-gaps, so that there will be extended arcs of approach and recession, particularly the latter, and, when one tooth is passing out of-the field, another tooth will be entering the arc of recession and commencing to leave. Hence, two or more teeth will always lie along the path of recession at the same time, the number of teeth will not fluctuate, and it is of further importance that the rate of approach or recession as measured by the rate of chan e in the -magnetic pull which is proportiona to the square of the magnetic flux should be uniform, or that the sum of the pulls due to the magnetic'fiux to all of the teeth should be a constant quantity. This has been efiected by suitable adjustment of the air-gap along this are based on the rinciple that the magnetic pull is inversel y proportional to the square of the air-gap.

In the specific example herein shown, it is intended to produce a field which embraces an arc of about 151 degrees, in which 32 dei grees is an arc of approach, 87 degrees of the eld is to be uniform, and about 32 degrees is an arc of recession. Three teeth always lie along the arc of ap roach and also along the arc of recession. n theillustrated example there are thirty-five teeth in the armature and three teeth subtend an an le of slightly less than 32 degrees, which is ere assumed for convenience of subdivision and calcula-' tion. Since the grade of the tempered sections of approach and recession is slight at points immediately adjoining the uniform section, the discrepancy is negligible. The air-gap ismade 0.050.OV6I' the uniform portion. The magnetic pull through thearmature teeth commences or ends at the point a,

where it is zero, and becomes uniform after passing the point e. If the magnetic pull at e berepresented by 4, then the air-gap is graded to give at the equally spaced intermediate points I) 0 cl values in arithmetical ratio as 1 2 3. The relative air-gaps at c d e are respectively 0.071, 0.058, 0.050. The reciprocals of the squares of these numbers are in the proportional relations of 2 3 4;. Hence the reciprocal of the square of the air-gap length bears a constant ratio to the distance along the armature periphery from the fixed point a.

In the curve diagram, the point a is laced at the origin. The axis X represents tli face of the armature, the curve is the develo ed face of that part of the pole-horn whic is used as an arc of approach or-recession, and the ordinates represent the air- This is accomplished by gap. The ordinates are drawn to an exaggerated scale to accentuate and better illustrate the peculiarities of the curve of inverse squares. The curve is represented by the equation tance from a in degrees, and y represents the theoretical air-gap in inches or decimals of an inch. This curve is represented by the line b c d e, and the pole-face r s t it conforms to this line except near the tip, where, since the lines of force are not approximately radial and do not lie along the ordinates, but scatter, an empirical modification by cutting back or turning up the nose of the tip from the curve or inverse squares is necessary in order to continue the uniform increase or diminution of magnetic pull or flux squared per de ree of angle, or to so adjust the magnetic ux that the sum of the squares of the magnetic flux to all of the teeth will be a constant quantity as the armature revolves. For the convenience of the die-maker in constructing a die to cut out the blanks for the pole-shoe, this required curve has been very closely approximated by extending the circular are 'r 0 r of uniform intensity which is struck from the armature center with a radius of 3.050 through 82 degrees, with tangent arcs of 3.480 radius which envelop the armature through arcs 1" s of 15 degrees each, thence continuing the surface with the tangents s t to the latter arcs till they meet reverse curves in of 0.410 radius, the centers of which are on radial lines 8%- degrees further around the armature. This graduation of the air-gap, whereby audible vibration is overcome, 1s effective with machines of other types than that specifically illustrated herein, and I do not limit myself in this feature of the invention either to an inclosing yoke, or to the ada tation of the dimensions of the cores for t e same urpose.

The open ends of the yoke have attached to them end-shields 7 7 which complete the inclosure of the electrical parts and carry bearings for the armature-shaft and su ort the brushes and other parts, the deta1 s of which are fully set forth in my United States Patent No. 792,762, dated June 20, 1905. As the novel features of these parts are therein claimed, they are not herein set forth in detail.

Machines such as are herein set forth have been manufactured in large quantities and are found to be free from objectionable audible vibration.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A dynamo-electric machine having an air-gap section in which the reciprocal of the square of the air-gap length bears a constant ratio to the distance along the armature periphery from a fixed point, substantially as I described.

2. A dynamo-electric machine having an air-gap section at intermediate portions of which the reciprocal of the square of the airgap length bears a constant ratio to the distance along the armature periphery from a fixed point, and near the wider end of which the gap is further increased to eiiect throughout a change in the square of the magnetic flux which bears a constant ratio to the distance along the armature periphery from said fixed point, substantially as described.

3. A dynamo-electric machine having a toothed armature and an air gap between the armature and field with graduated terminal sections wherein the reciprocal of the square of the air-gap length bears a constant ratio to the distance along the armature periphery from a fixed point, each terminal section being extended over an arc which'is the same as that embracing several teeth, substantially. as described.

4. A dynamo-electric machine having a toothed armature and an air gap between the armature and field with graduated terminal sections wherein the reciprocal of the square of the air-gap length bears a constant ratio to the distance along the armature periphery from a fixed oint and wherein the gap is further increase near the wider ends to efiect throughout each terminal section a change in the square of the magnetic flux which bears a constant ratio to the distance along the armature periphery from said fixed point, each terminal section being extended over an are which is the same as that en1brac ing several teeth, substantially as described.

5. A dynamo-electric machine having an air gap with graduated terminal sections wherein the reciprocal of the square of the air-gap length bears a constant ratio to the distance along the armature periphery from a fixed point, and a pole the core of which is elongated in the direction of the circumference of the machine, substantially as described.

6. A dynamo-electric machine having an air-gap with graduated terminal sections wherein the reciprocal of the square of the air-gap length bears a constant ratio to the distance along the armature periphery from a fixed point and wherein the gap is further increased near the wider ends to effect throughout each terminal section a change in the square of the magnetic fiux which bears a constant ratio to the distance along the armature peri hery from said fixed point, each termina section being extended over an are which is the same as that embracing several teeth, and a pole the core of which is elongated in the direction of the circumference of the machine, substantially as described.

Signed by me at East Orange, New Jersey, February 10, 1905.

GANO S. DUNN.

Witnesses:

HOWARD M. GASSMAN, MARY E. SAMMIs. 

